Resource selection method for v2x operation of terminal in wireless communication system, and terminal using method

ABSTRACT

Provided are a resource selection method for a vehicle-to-everything (V2X) operation of a terminal in a wireless communication system, and a terminal using the method. The method comprises: monitoring physical sidelink control channels (PSCCHs) for other terminals in a first subframe; and transmitting, in a second subframe, a V2X message by using a resource which is not overlapped with a resource scheduled by the PSCCH for another terminal.

BACKGROUND OF THE INVENTION Field of the invention

The present invention relates to a method for selecting a resource forv2x operation by a wireless device in a wireless communication system,and to a wireless device performing the method.

Related Art

In International Telecommunication Union Radio communication sector(ITU-R), a standardization task for International MobileTelecommunication (IMT)-Advanced, that is, the next-generation mobilecommunication system since the third generation, is in progress.IMT-Advanced sets its goal to support Internet Protocol (IP)-basedmultimedia services at a data transfer rate of 1 Gbps in the stop andslow-speed moving state and of 100 Mbps in the fast-speed moving state.

For example, 3^(rd) Generation Partnership Project (3GPP) is a systemstandard to satisfy the requirements of IMT-Advanced and is preparingfor LTE-Advanced improved from Long Term Evolution (LTE) based onOrthogonal Frequency Division Multiple Access (OFDMA)/SingleCarrier-Frequency Division Multiple Access (SC-FDMA) transmissionschemes. LTE-Advanced is one of strong candidates for IMT-Advanced.

There is a growing interest in a Device-to-Device (D22) technology inwhich devices perform direct communication. In particular, D2D has beenin the spotlight as a communication technology for a public safetynetwork. A commercial communication network is rapidly changing to LTE,but the current public safety network is basically based on the 2Gtechnology in terms of a collision problem with existing communicationstandards and a cost. Such a technology gap and a need for improvedservices are leading to efforts to improve the public safety network.

The public safety network has higher service requirements (reliabilityand security) than the commercial communication network. In particular,if coverage of cellular communication is not affected or available, thepublic safety network also requires direct communication betweendevices, that is, D2D operation.

D2D operation may have various advantages in that it is communicationbetween devices in proximity For example, D2D UE has a high transferrate and a low delay and may perform data communication. Furthermore, inD2D operation, traffic concentrated on a base station can bedistributed. If D2D UE plays the role of a relay, it may also play therole of extending coverage of a base station.

Meanwhile, the D2D operation may also be applied tovehicle-to-everything (V2X) communication. The V2X communication refersto communication technology with vehicles via all interfaces.Embodiments of V2X include, for example, vehicle-to-vehicle (V2V),vehicle-to-infrastructure (V2I), vehicle-to-person (V2P) communications,and the like.

When a first wireless device performs V2X communication with a secondwireless device, and if the second wireless device also transmits asignal using the same or partially overlapped resource as that used bythe first wireless device, this may cause mutual interference, and,thus, reliable V2X communication will be difficult to perform. Forexample, resources for V2X communication are supplied in the form of aresource pool. In fact, resources used to perform V2X communication maybe selected from the resource pool by wireless devices. In this case,because different wireless devices arbitrarily choose their ownresources from the same resource pool, the same or partially overlappingresources from each other may be selected by the different wirelessdevices.

Thus, a method for efficiently selecting resources for V2X operation anda wireless device performing the above method are needed.

SUMMARY OF THE INVENTION

The present invention provides a method for selecting a resource for aV2X operation by a wireless device in a wireless communication systemand a wireless device configured to perform the method.

In one aspect, provided is a method for performing avehicle-to-everything (V2X) operation by a user equipment (UE) in awireless communication system. The method includes monitoring a physicalsidelink control channel (PSCCH) for an another UE on a first subframeand transmitting a V2X message using a resource that does not overlapwith a resource scheduled by the PSCCH for the another UE on a secondsubframe.

The UE may receive, from a network, information on a PSCCH subframe poolindicating subframes where the UE can transmit the PSCCH.

The second subframe may be included in the subframes indicated by theinformation on the PSCCH subframe pool.

The UE may monitor a PSCCH for the another UE as moving a basic resourceunit composed of at least one subframe by one subframe.

The UE may monitor an idle resource unit that does not overlap with aresource scheduled by the PSCCH for the another UE.

When a plurality of idle resource units are detected, the UE may selectone idle resource unit among the plurality of idle resource units andtransmits a PSCCH.

In another aspect, provided is a user equipment (UE) for performing avehicle-to-everything (V2X) operation in a wireless communicationsystem. The UE includes a RF (radio frequency) unit configured totransmit and receive a RF signal and a processor operatively coupled tothe RF unit. The processor monitors a physical sidelink control channel(PSCCH) for an another UE on a first subframe and transmits a V2Xmessage using a resource that does not overlap with a resource scheduledby the PSCCH for the another UE on a second subframe.

In accordance with the present disclosure, while a wireless device movesa resource region called a basic resource unit along a temporal region,the wireless device monitors whether another wireless device usesresources in the basic resource unit. Thus, the device detects and usesidle resource units that are not used by said another wireless device,interference with said another wireless device can be reduced. Further,when a plurality of idle resource units are detected by the device andsaid another wireless device may also use the plurality of idle resourceunits, the device may choose a specific idle resource unit whileavoiding resource-collision with said another wireless device. Thisincreases the reliability of the V2X operation and the efficiency ofresource usage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane.

FIG. 3 is a diagram showing a wireless protocol architecture for acontrol plane.

FIG. 4 shows a basic structure for ProSe.

FIG. 5 shows the deployment examples of types of UE performing ProSedirect communication and cell coverage.

FIGS. 6 and 7 show examples of defining V2X transmission resourcecandidates while sliding the basic resource unit.

FIG. 8 illustrates a method for selecting a resource for a V2X operationby a wireless device, according to one embodiment of the presentdisclosure.

FIG. 9 shows a specific example in which a wireless device selects aresource for a V2X operation.

FIG. 10 illustrates signaling between a first wireless device and a basestation in order to transmit a V2X message.

FIG. 11 is a block diagram illustrating a wireless device in which anembodiment of the present disclosure is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless communication system.

The wireless communication system may be referred to as an Evolved-UMTSTerrestrial

Radio Access Network (E-UTRAN) or a Long Term Evolution (LTE)/LTE-Asystem, for example.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane. FIG. 3 is a diagram showing a wireless protocol architecture fora control plane. The user plane is a protocol stack for user datatransmission. The control plane is a protocol stack for control signaltransmission.

Referring to FIGS. 2 and 3, a PHY layer provides an upper layer with aninformation transfer service through a physical channel. The PHY layeris connected to a medium access control (MAC) layer which is an upperlayer of the PHY layer through a transport channel. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how and with whatcharacteristics data is transferred through a radio interface.

Data is moved between different PHY layers, that is, the PHY layers of atransmitter and a receiver, through a physical channel The physicalchannel may be modulated according to an Orthogonal Frequency DivisionMultiplexing (OFDM) scheme, and use the time and frequency as radioresources.

The functions of the MAC layer include mapping between a logical channeland a transport channel and multiplexing and demultiplexing to atransport block that is provided through a physical channel on thetransport channel of a MAC Service Data Unit (SDU) that belongs to alogical channel The MAC layer provides service to a Radio Link Control(RLC) layer through the logical channel.

The functions of the RLC layer include the concatenation, segmentation,and reassembly of an RLC SDU. In order to guarantee various types ofQuality of Service (QoS) required by a Radio Bearer (RB), the RLC layerprovides three types of operation mode: Transparent Mode (TM),Unacknowledged Mode (UM), and Acknowledged Mode (AM). AM RLC provideserror correction through an Automatic Repeat Request (ARQ).

The RRC layer is defined only on the control plane. The RRC layer isrelated to the configuration, reconfiguration, and release of radiobearers, and is responsible for control of logical channels, transportchannels, and PHY channels. An RB means a logical route that is providedby the first layer (PHY layer) and the second layers (MAC layer, the RLClayer, and the PDCP layer) in order to transfer data between UE and anetwork.

The function of a Packet Data Convergence Protocol (PDCP) layer on theuser plane includes the transfer of user data and header compression andciphering. The function of the PDCP layer on the user plane furtherincludes the transfer and encryption/integrity protection of controlplane data.

What an RB is configured means a process of defining the characteristicsof a wireless protocol layer and channels in order to provide specificservice and configuring each detailed parameter and operating method. AnRB can be divided into two types of a Signaling RB (SRB) and a Data RB(DRB). The SRB is used as a passage through which an RRC message istransmitted on the control plane, and the DRB is used as a passagethrough which user data is transmitted on the user plane.

If RRC connection is established between the RRC layer of UE and the RRClayer of an E-UTRAN, the UE is in the RRC connected state. If not, theUE is in the RRC idle state.

A downlink transport channel through which data is transmitted from anetwork to UE includes a broadcast channel (BCH) through which systeminformation is transmitted and a downlink shared channel (SCH) throughwhich user traffic or control messages are transmitted. Traffic or acontrol message for downlink multicast or broadcast service may betransmitted through the downlink SCH, or may be transmitted through anadditional downlink multicast channel (MCH). Meanwhile, an uplinktransport channel through which data is transmitted from UE to a networkincludes a random access channel (RACH) through which an initial controlmessage is transmitted and an uplink shared channel (SCH) through whichuser traffic or control messages are transmitted.

Logical channels that are placed over the transport channel and that aremapped to the transport channel include a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), and a multicast trafficchannel (MTCH).

The physical channel includes several OFDM symbols in the time domainand several subcarriers in the frequency domain. One subframe includes aplurality of OFDM symbols in the time domain. An RB is a resourcesallocation unit, and includes a plurality of OFDM symbols and aplurality of subcarriers. Furthermore, each subframe may use specificsubcarriers of specific OFDM symbols (e.g., the first OFDM symbol) ofthe corresponding subframe for a physical downlink control channel(PDCCH), that is, an L1/L2 control channel. A Transmission Time Interval(TTI) is a unit time for subframe transmission.

The RRC state means whether or not the RRC layer of UE is logicallyconnected to the RRC layer of the E-UTRAN. A case where the RRC layer ofUE is logically connected to the RRC layer of the E-UTRAN is referred toas an RRC connected state. A case where the RRC layer of UE is notlogically connected to the RRC layer of the E-UTRAN is referred to as anRRC idle state. The E-UTRAN may check the existence of corresponding UEin the RRC connected state in each cell because the UE has RRCconnection, so the UE may be effectively controlled. In contrast, theE-UTRAN is unable to check UE in the RRC idle state, and a Core Network(CN) manages UE in the RRC idle state in each tracking area, that is,the unit of an area greater than a cell. That is, the existence ornon-existence of UE in the RRC idle state is checked only for each largearea. Accordingly, the UE needs to shift to the RRC connected state inorder to be provided with common mobile communication service, such asvoice or data.

When a user first powers UE, the UE first searches for a proper cell andremains in the RRC idle state in the corresponding cell. The UE in theRRC idle state establishes RRC connection with an E-UTRAN through an RRCconnection procedure when it is necessary to set up the RRC connection,and shifts to the RRC connected state. A case where UE in the RRC idlestate needs to set up RRC connection includes several cases. Forexample, the cases may include a need to send uplink data for a reason,such as a call attempt by a user, and to send a response message as aresponse to a paging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

In the NAS layer, in order to manage the mobility of UE, two types ofstates: EPS Mobility Management-REGISTERED (EMM-REGISTERED) andEMM-DEREGISTERED are defined. The two states are applied to UE and theMME. UE is initially in the EMM-DEREGISTERED state. In order to access anetwork, the UE performs a process of registering it with thecorresponding network through an initial attach procedure. If the attachprocedure is successfully performed, the UE and the MME become theEMM-REGISTERED state.

In order to manage signaling connection between UE and the EPC, twotypes of states: an EPS Connection Management (ECM)-IDLE state and anECM-CONNECTED state are defined. The two states are applied to UE andthe MME. When the UE in the ECM-IDLE state establishes RRC connectionwith the E-UTRAN, the UE becomes the ECM-CONNECTED state. The MME in theECM-IDLE state becomes the ECM-CONNECTED state when it establishes S1connection with the E-UTRAN. When the UE is in the ECM-IDLE state, theE-UTRAN does not have information about the context of the UE.Accordingly, the UE in the ECM-IDLE state performs procedures related toUE-based mobility, such as cell selection or cell reselection, without aneed to receive a command from a network. In contrast, when the UE is inthe ECM-CONNECTED state, the mobility of the UE is managed in responseto a command from a network. If the location of the UE in the ECM-IDLEstate is different from a location known to the network, the UE informsthe network of its corresponding location through a tracking area updateprocedure.

The D2D operation will now be described. In 3GPP LTE-A, the servicerelated to D2D operation is called proximity based service (ProSe).Hereinafter, ProSe is equivalent to D2D operation and ProSe may beinterchanged with D2D operation. ProSe will now be described.

The ProSe includes ProSe direction communication and ProSe directdiscovery. The ProSe direct communication is communication performedbetween two or more proximate UEs. The UEs may perform communication byusing a protocol of a user plane. A ProSe-enabled UE implies a UEsupporting a procedure related to a requirement of the ProSe. Unlessotherwise specified, the ProSe-enabled UE includes both of a publicsafety UE and a non-public safety UE. The public safety UE is a UEsupporting both of a function specified for a public safety and a ProSeprocedure, and the non-public safety UE is a UE supporting the ProSeprocedure and not supporting the function specified for the publicsafety.

ProSe direct discovery is a process for discovering anotherProSe-enabled UE adjacent to ProSe-enabled UE. In this case, only thecapabilities of the two types of ProSe-enabled UE are used. EPC-levelProSe discovery means a process for determining, by an EPC, whether thetwo types of ProSe-enabled UE are in proximity and notifying the twotypes of ProSe-enabled UE of the proximity.

Hereinafter, for convenience, the ProSe direct communication may bereferred to as D2D communication, and the ProSe direct discovery may bereferred to as D2D discovery.

FIG. 4 shows a basic structure for ProSe.

Referring to FIG. 4, the basic structure for ProSe includes an E-UTRAN,an EPC, a plurality of types of UE including a ProSe applicationprogram, a ProSe application server (a ProSe APP server), and a ProSefunction.

The EPC represents an E-UTRAN core network configuration. The EPC mayinclude an MME, an S-GW, a P-GW, a policy and charging rules function(PCRF), a home subscriber server (HSS) and so on.

The ProSe APP server is a user of a ProSe capability for producing anapplication function. The ProSe APP server may communicate with anapplication program within UE. The application program within UE may usea ProSe capability for producing an application function.

The ProSe function may include at least one of the followings, but isnot necessarily limited thereto.

Interworking via a reference point toward the 3rd party applications

Authorization and configuration of UE for discovery and directcommunication

Enable the functionality of EPC level ProSe discovery

ProSe related new subscriber data and handling of data storage, and alsohandling of the ProSe identities

Security related functionality

Provide control towards the EPC for policy related functionality

Provide functionality for charging (via or outside of the EPC, e.g.,offline charging)

A reference point and a reference interface in the basic structure forProSe are described below.

PC1: a reference point between the ProSe application program within theUE and the ProSe application program within the ProSe APP server. Thisis used to define signaling requirements in an application dimension.

PC2: a reference point between the ProSe APP server and the ProSefunction. This is used to define an interaction between the ProSe APPserver and the ProSe function. The update of application data in theProSe database of the ProSe function may be an example of theinteraction.

PC3: a reference point between the UE and the ProSe function. This isused to define an interaction between the UE and the ProSe function. Aconfiguration for ProSe discovery and communication may be an example ofthe interaction.

PC4: a reference point between the EPC and the ProSe function. This isused to define an interaction between the EPC and the ProSe function.The interaction may illustrate the time when a path for 1:1communication between types of UE is set up or the time when ProSeservice for real-time session management or mobility management isauthenticated.

PC5: a reference point used for using control/user plane for discoveryand communication, relay, and 1:1 communication between types of UE.

PC6: a reference point for using a function, such as ProSe discovery,between users belonging to different PLMNs.

SGi: this may be used to exchange application data and types ofapplication dimension control information.

The D2D operation may be supported both when UE is serviced within thecoverage of a network (cell) or when it is out of coverage of thenetwork.

FIG. 5 shows the deployment examples of types of UE performing ProSedirect communication and cell coverage.

Referring to FIG. 5(a), types of UE A and B may be placed outside cellcoverage. Referring to FIG. 5(b), UE A may be placed within cellcoverage, and UE B may be placed outside cell coverage. Referring toFIG. 5(c), types of UE A and B may be placed within single cellcoverage. Referring to FIG. 5(d), UE A may be placed within coverage ofa first cell, and UE B may be placed within coverage of a second cell.

ProSe direct communication may be performed between types of UE placedat various positions as in FIG. 5.

<Radio Resource Allocation for D2D Communication (ProSe DirectCommunication)>.

At least one of the following two modes may be used for resourceallocation for D2D communication.

1. Mode 1

Mode 1 is mode in which resources for ProSe direct communication arescheduled by an eNB. UE needs to be in the RRC_CONNECTED state in orderto send data in accordance with mode 1. The UE requests a transmissionresource from an eNB. The eNB performs scheduling assignment andschedules resources for sending data. The UE may send a schedulingrequest to the eNB and send a ProSe Buffer Status Report (BSR). The eNBhas data to be subjected to ProSe direct communication by the UE basedon the ProSe BSR and determines that a resource for transmission isrequired.

2. Mode 2

Mode 2 is mode in which UE directly selects a resource. UE directlyselects a resource for ProSe direct communication in a resource pool.The resource pool may be configured by a network or may have beenpreviously determined.

Meanwhile, if UE has a serving cell, that is, if the UE is in theRRC_CONNECTED state with an eNB or is placed in a specific cell in theRRC_IDLE state, the UE is considered to be placed within coverage of theeNB.

If UE is placed outside coverage, only mode 2 may be applied. If the UEis placed within the coverage, the UE may use mode 1 or mode 2 dependingon the configuration of an eNB.

If another exception condition is not present, only when an eNB performsa configuration, UE may change mode from mode 1 to mode 2 or from mode 2to mode 1.

<D2D Discovery (ProSe Direct Discovery)>

D2D discovery refers to the procedure used in a ProSe capable terminaldiscovering other ProSe capable terminals in close proximity thereto andmay be referred to as ProSe direct discovery. The information used forProSe direct discovery is hereinafter referred to as discoveryinformation.

A PC 5 interface may be used for D2D discovery. The PC 5 interfaceincludes an MAC layer, a PHY layer, and a ProSe Protocol layer, that is,a higher layer. The higher layer (the ProSe Protocol) handles thepermission of the announcement and monitoring of discovery information.The contents of the discovery information are transparent to an accessstratum (AS). The ProSe Protocol transfers only valid discoveryinformation to the AS for announcement. The MAC layer receives discoveryinformation from the higher layer (the ProSe Protocol). An IP layer isnot used to send discovery information. The MAC layer determines aresource used to announce discovery information received from the higherlayer. The MAC layer produces an MAC protocol data unit (PDU) forcarrying discovery information and sends the MAC PDU to the physicallayer. An MAC header is not added.

In order to announce discovery information, there are two types ofresource assignment.

1. Type 1

The type 1 is a method for assigning a resource for announcing discoveryinformation in a UE-not-specific manner An eNB provides a resource poolconfiguration for discovery information announcement to types of UE. Theconfiguration may be broadcasted through the SIB. The configuration maybe provided through a UE-specific RRC message. Or the configuration maybe broadcasted through other than the RRC message in other layer or maybe provided by UE-specific signaling.

UE autonomously selects a resource from an indicated resource pool andannounces discovery information using the selected resource. The UE mayannounce the discovery information through a randomly selected resourceduring each discovery period.

2. Type 2

The type 2 is a method for assigning a resource for announcing discoveryinformation in a UE-specific manner UE in the RRC_CONNECTED state mayrequest a resource for discovery signal announcement from an eNB throughan RRC signal. The eNB may announce a resource for discovery signalannouncement through an RRC signal. A resource for discovery signalmonitoring may be assigned within a resource pool configured for typesof UE.

An eNB 1) may announce a type 1 resource pool for discovery signalannouncement to UE in the RRC_IDLE state through the SIB. Types of UEwhose ProSe direct discovery has been permitted use the type 1 resourcepool for discovery information announcement in the RRC_IDLE state.Alternatively, the eNB 2) announces that the eNB supports ProSe directdiscovery through the SIB, but may not provide a resource for discoveryinformation announcement. In this case, UE needs to enter theRRC_CONNECTED state for discovery information announcement.

An eNB may configure that UE has to use a type 1 resource pool fordiscovery information announcement or has to use a type 2 resourcethrough an RRC signal in relation to UE in the RRC_CONNECTED state.

Now, the present invention will be described. The above-described D2Doperation may also be applied to a V2X (VEHICLE-TO-EVERYTHING,VEHICLE-TO-X) operation.

In V2X operation, ‘X’ may be a pedestrian. In this case, V2X can berepresented as V2P. The V2P communications refers to the communicationbetween a vehicle (or a wireless device installed in a vehicle) and aperson-carrying device. The term “person-carrying device” may refer to awireless device carried by the pedestrian, a wireless device held by acyclist, and a wireless device that a driver of a slow moving vehiclecarries.

Alternatively, X may be a vehicle. In this case, V2X may be representedas V2V. Alternatively, X may be an infrastructure or a network. In thiscase, V2X may be represented as V2I and V2N, respectively. Theinfrastructure includes a roadside unit (RSU) to indicate speed, and adevice to indicate the traffic environment. The infrastructure mayoperate as a base station or operate as a wireless device.

Hereinafter, for convenience of explanation of the schemes proposed bythe present invention, a V2P communication-related device possessed by apedestrian is referred to as a P-UE, while a V2X communication-relateddevice installed in the vehicle is referred to as a V-UE. The ‘entity’may be interpreted as P-UE and/or V-UE and/or RSU (ornetwork/infrastructure).

Hereinafter, a wireless device transmitting a V2X message may bereferred to as a V2X TX UE or a V2X transmission wireless device. Theschemes proposed below present a method for allowing different wirelessdevices transmitting V2X messages to efficiently select V2X transmissionresources from a pre-defined or pre-signaled V2X transmission resourcepool (V2X TX resource pool). In other words, in one example, a V2Xtransmission wireless device may arbitrarily select a V2X transmissionresource from a configured (signaled) V2X transmission resource pool andtransmit a V2X message using the selected V2X transmission resource. TheV2X message may be, for example, a D2D discovery message, a D2Dcommunication message, or the like.

In the present disclosure, the term “energy sensing (or detection)” mayrefer to RSRP measurement operation for a pre-configured or pre-signaledreference signal (for example, DMRS) on the PSSCH resource regionscheduled by the PSCCH as blind-decoded or blind-detected; and/or, tomeasurement of a linear average of RSSI (for symbols) on apre-configured or pre-signaled resource unit (or region) (for example,basic resource unit).

Applying the present invention can reduce the probability that differentV2X transmission wireless devices may transmits V2X messages using V2Xtransmission resources partially or wholly overlapping each other.

In the present invention, while a V2X transmission wireless deviceslides or move a basic resource unit having a size or window aspre-defined or signaled from a network or a serving base station, from aspecific timing (e.g., subframe#N, as denoted SF#), the V2X transmissionwireless device may define V2X transmission resource candidates relatedto V2X message transmission. Here, the V2X transmission wireless devicemay be interpreted as carrying out its own V2X (data and/or control)message transmission using the corresponding basic resource unit (aspre-configured or pre-signaled).

Here, a basic resource unit (or window) may be composed of combinationsof temporal region resources (for example, subframe, slot, symbol)and/or frequency region resources (for example, physical resource blocks(pairs), subcarriers). For example, a basic resource unit may becomposed of N subframes, and N may be a natural number of 1 or more. Forexample, the basic resource unit may be composed of one subframe and aplurality of physical resource blocks (PRBs) configured or signaled inadvance. For example, the sliding size may be configured (or signaled)to be equal to the number of subframes constituting the basic resourceunit.

FIGS. 6 and 7 show examples of defining V2X transmission resourcecandidates while sliding the basic resource unit.

FIG. 6 is an example of a case where a V2X control message transmissionresource region and a V2X data message transmission resource region areimplemented in a TDM form. FIG. 7 is an example of a case where a V2Xcontrol message transmission resource region and a V2X data messagetransmission resource region are implemented in a FDM form.

In FIG. 6 and FIG. 7, the basic resource unit is composed of fourconsecutive subframes. In this connection, in one example, a unit bywhich the basic resource unit is moved is defined as a sliding size. InFIG. 6 and FIG. 7, it is assumed that the sliding size is one subframe.

The sensing (or monitoring) window (size) of the V2X transmissionwireless device may be configured (or signaled) as: 1) an interval fromSF#(N−K) to SF#(N−1) (for example, K value is a positive integer equalto or greater than 1, and setting the interval in this way is calledoption#A); and/or 2) an interval from SF#(N−K1) to SF#(N−K2) (forexample, ‘K1’ and ‘K2’ are positive integers greater than or equal to 1,and setting the interval in this way is called option#B; for example, inthat K2 is not fixed to 1, the option#B differs from option#A) takinginto further consideration of the decoding/encoding delay (which may beinterpreted as including times related to, for example,sensing/detection operation, and/or its own (optimal) transmissionresource selection operation based on the sensing/detection operation,and/or V2X message-related processing). In this connection, in oneexample, a V2X transmission wireless device may perform blind decoding(or detection) for a V2X control message (information) from another V2Xtransmission wireless device, and for (V2X) data resource-relatedinformation scheduled by the corresponding V2X control message, in a V2Xcontrol message transmission resource region (named “CTL_REGION”)belonging to the corresponding sensing or monitoring.

Additionally and alternatively, using the blind decoding (or detection)operation (within the sensing (or monitoring) window described above),the V2X transmission wireless device acquires another V2X transmissionwireless device-related V2X control message (information) and (V2X) dataresource region information scheduled by the corresponding V2X controlmessage, and, subsequently, the V2X transmission wireless device mayalso perform an energy detection (sensing) operation for the V2Xtransmission data resource (or subframe) region of another V2X devicewith the V2X control message as blind decoded or detected in a timeinterval and/or resource region (for example, a subframe (resource)interval as exemplified in option#A or option#B) as pre-defined orsignaled from the network or the serving base station.

In one example, it may be assumed in FIG. 6 and FIG. 7, the resourceregion (or size/unit), which is used by the V2X transmission wirelessdevice to perform the following operations: sensing (or detection)operation (for example, another V2X transmission wireless device-relatedV2X control message blind decoding/detection operation), energydetection/sensing operation) (for the V2X data transmission resourceregion that the corresponding V2X control message schedules) may be thesame as the basic resource unit (size) used for V2X data and/or controlmessage transmission.

In one example, after the sensing (or detection) operation, the V2Xtransmission wireless device may determine whether to perform the finalV2X message transmission at the time of SF#N based on absence orpresence and/or, if any, a number of an idle basic resource unit(s) (oridle resource unit(s)) satisfying the following additional conditions orall conditions at the time of SF#N. In this connection, in one example,the corresponding idle resource unit (candidate) selection or decisionoperation may include excluding a transmission resource candidate inwhich a partial or complete collision or overlap may occur betweendifferent V2X TX wireless devices at a relatively high probability fromthe entire transmission resource candidate. In this connection, in oneexample, the V2X transmission wireless device may perform a blinddecoding/detection operation for another V2X transmission wirelessdevice-related V2X control message in ‘CTL_REGION’ belonging to thepre-defined or signaled time/resource interval prior to ‘SF#N’. In otherwords, in one example, the V2X transmission wireless device may performthe corresponding sensing/detection operation to monitor anotherwireless device-related V2X control message. In this way, in oneexample, in the subsequent time/resource interval including ‘SF#N’, theV2X transmission wireless device may be able to identify informationabout the resources used for V2X data message transmission by anotherV2X transmission wireless device of interest, for example, thelocation/number of subframes or resource blocks, and/or the number ofrepeated transmissions thereof.

The ‘K’ and/or ‘K1’ and/or ‘K2’ values may be pre-defined or signaledfrom the network or serving base station.

In FIGS. 6 and 7, it may be considered that the value of ‘K’ and/or ‘K1’and/or ‘K2’ is set to ‘1’.

In other words, in one example, the V2X transmission wireless devicethat performs V2X message transmission on subframe#N monitors anotherwireless device-related V2X control message on subframe#N−1. The V2Xtransmission wireless device may identify the location/number ofresources used for V2X message transmission by said another wirelessdevice and/or repeated transmission number thereof in the subsequentsubframe/resources including subframe#N. As a result, the V2Xtransmission wireless device determines a resource that is not used bysaid another wireless device as its idle resource unit candidate.

The idle resource unit candidate described above may be selected ordetermined according to whether one or both of the following twoexemplary conditions are satisfied.

(Example#1) In one example, (while the V2X transmission device performsblind decoding or detection on another V2X transmission wirelessdevice-related V2X control message within the sensing/monitoring windowdescribed above), the V2X transmission device may determine as an idleresource unit candidate a basic resource unit that does not partially orwholly overlap with the resources used for V2X data and/or controlmessage transmission by said another V2X transmission wireless device ofinterest.

(Example#2) In one example, (on another V2X transmission wirelessdevice-related V2X data transmission resource/subframe regions accordingto the blind-decoded or blind-detected V2X control message) the V2Xtransmission device may determine as an idle resource unit (candidate) abasic resource unit for which detected/sensed energy has an (average)value less than a (average) threshold as pre-defined or signaled (fromthe network or serving base station).

In FIGS. 6 and 7, in one example, the total number of basic resourceunits, i.e., idle resource units, satisfying the condition of theExample#1 at the time of SF#N is two.

On the other hand, when option#B is applied, the V2X transmissionwireless device may not be able to perform a blind decoding or detectionoperation in the CTL_REGION belonging to the interval from SF#(N−K2+1)to SF#(N−1) in consideration of decoding/encoding delay. Thedecoding/encoding delay may include, for example, sensing/detectionoperation delay time, and/or optimal transmission resource selectionoperation delay time according to the detection/detection operationresult, and/or V2X message-related processing time. Therefore, the V2Xtransmission wireless device performs blind decoding in ‘CTL_REGION’belonging to the interval from SF#(N−K1) to SF#(N−K2). Then, the V2Xtransmission wireless device adds the pre-defined or signaled offsetvalue OFF_VAL to the number M of idle resource units at the SF#N timepoint derived via such blind decoding, thereby to calculate/derive thenumber M+OFF_VAL of idle resource units at the SF#N time point.

Using the application of these rules, the change of the number of idleresource units at the SF#N time point may be reflected to some extentdue to the V2X control and/or data message transmission by another V2Xtransmission wireless device of interest as occurs in the interval fromSF#(N−K2+1) to SF#(N−1), that is, in the CTL_REGION region where blinddecoding is not performed.

FIG. 8 illustrates a method for selecting a resource for a V2X operationby a wireless device, according to one embodiment of the presentdisclosure.

Referring to FIG. 8, the wireless device monitors PSCCHs for otherwireless devices in a first subframe S210. The PSCCH (physical sidelinkcontrol channel) means the control channel of the side link between thewireless devices. In this connection, the first subframe may be asubframe belonging to the basic resource unit as described in FIGS. 6and 7. Also, the first subframe may be a subframe before the secondsubframe on which the wireless device performs the V2X transmission.

The wireless device transmits a V2X message on the second subframe usinga resource that does not overlap with the PSSCH resource scheduled bythe PSCCHs for another wireless device, that is, using an idle resourceunit S220.

FIG. 9 shows a specific example in which a wireless device selects aresource for a V2X operation.

Referring to FIG. 9, while the wireless device moves the basic resourceunit composed of at least one subframe by one subframe, the wirelessdevice monitors PSCCHs for other wireless devices at step S410.

The wireless device searches for an idle resource unit that does notoverlap with the PSSCH resource scheduled by the PSCCHs for the otherwireless devices, that is, searches S420. If the number of the idleresource units is plural and/or is larger than the pre-configured orpre-signaled threshold value, the idle resource unit to be actually usedfor transmitting the PSSCH and/or PSCCH is determined S430.

Although the above rules (for example, Example#1, Example#2) areapplied, the location and/or number of idle resource units assumed bydifferent V2X transmission wireless devices may be the same at specificpoint SF#N. In this case, different V2X wireless devices may transmitV2X messages using the same idle resource unit, in which case resourceconflicts may occur. Additional methods may be needed to lower theprobability that the device selects, among the plurality of idleresource units, an idle resource unit which is partially or whollyoverlapped with a V2X transmission resource used by another wirelessdevice, when the V2X transmission wireless device finally chooses a V2Xtransmission resource. The methods#1 to #5 proposed below propose thesemethods to lower the probability. Hereinafter, for the sake ofconvenience of explanation, the situation of FIG. 6 or FIG. 7 isassumed.

[Suggested method#1] The V2X transmission wireless device may beconfigured to perform the following operations: the probability that theV2X transmission and/or data message transmission will actually beperformed by the V2X transmission wireless device on a specific subframeSF#N may vary based on the number of idle resource unit candidates inthe corresponding subframe SF#N identified according to the aboveExample#1 and/or Example#2. For example, transmission probability valueP per an idle resource unit candidate may be configured or signaled. Ifthere are ‘M’ idle resource unit candidates in SF#N subframe, thewireless device may be configured to determine whether the V2X controland/or data message transmission may be performed on the correspondingsubframe SF#N at probability of P*M.

In one example, when the calculated value of ‘P*M’ is larger than ‘1’,the wireless device may be configured such that the V2X control and/ordata message transmission may performed on the ‘SF#N’ subframe at aprobability of ‘1’.

When the above [proposed method#1] is applied, in one example, if theV2X transmission wireless device actually performs V2X control and/ordata message transmission on the ‘SF#N’ subframe, the wireless devicemay be configured to randomly select one of the ‘M’ idle resource units,and/or to randomly select one of the idle resource units having arelatively small average detected/sensed energy value among the ‘M’ idleresource units.

When the above defined [suggested method#1] is applied, in one example,a V2X transmission wireless device may be configured as follows; if the‘idle resource unit’ does not exist in ‘SF#N’ subframe, V2X controland/or data message transmission may be omitted. Additionally oralternatively, one of all the basic resource units of the correspondingsubframe SF#N may be randomly selected and V2X control and/or datamessage transmission may be performed using this selected resource unit.Additionally or alternatively, one of the resource units having arelatively small average detected/sensed energy value among all thebasic resource units in the corresponding subframe SF#N may randomlyselected and the V2X control and/or data message transmission may beperformed using the selected one.

In the above [suggested method#1], the transmission probability valueper an idle resource unit may be configured or signaled independently orpartially or completely differently.

For example, there are three idle resource units (for example, idleresource unit#0, idle resource unit#1, idle resource unit#2) in the SF#Nsubframe, and the idle resource unit#0, idle resource unit#1 and idleresource unit#2 are configured or signaled, respectively to have theprobability values of P1, P2, P3. In this connection, the V2Xtransmission wireless device finally determines whether to perform theV2X control and/or data message transmission on the correspondingsubframe SF#N with the probability of P1+P2+P3.

In another example, when the [suggested method#1] described above isapplied, the transmission probability values per an idle resource unitmay be configured or signaled partially or completely differently orindependently between V2X messages/ information/service types, and/orV2X signals/ channels with different priorities.

The transmission probability value per an idle resource unit may beconfigured or signaled to be relatively higher with respect toinformation on incident occurrence and/or event occurrence-basedinformation or V2X synchronization signal with relatively high prioritythan with respect to other information or other V2X signal/channel withlow priority.

[Suggested method#2] The transmission probability value P per an idleresource unit may be configured or signaled for the V2X transmissionwireless device. The V2X transmission wireless device may be configuredto determine whether to perform the V2X control and/or data messagetransmission with an independent probability P for each idle resourceunit.

In this connection, in one example, the V2X control and/or data messagetransmissions using two or more idle resource units on the specificsubframe SF#N may be determined in relation to the probability. Then,the wireless device randomly selects one of the two or more idleresource units and performs the V2X control and/or data messagetransmission using the selected resource unit. Additionally oralternatively, the wireless device may be configured to randomly selectone of the idle resource units having a relatively small averagedetected or sensed energy value and to perform the V2X control and/ordata message transmission using the selected resource unit.

When the above defined [suggested method#2] is applied, in one example,a V2X transmission wireless device may be configured as follows; if the‘idle resource unit’ does not exist in ‘SF#N’ subframe, V2X controland/or data message transmission may be omitted. Additionally oralternatively, one of all the basic resource units in the correspondingsubframe SF#N may be randomly selected and the V2X control and/or datamessage transmission may be performed using this selected resource unit.Additionally or alternatively, one of the resource units having arelatively small average detected/sensed energy value among all thebasic resource units in the corresponding subframe SF#N may randomlyselected and the V2X control and/or data message transmission may beperformed using the selected one.

Additionally or alternatively, the V2X transmission wireless device maybe configured to determine, on a specific subframe SF#N, whether or notto perform the transmission of the V2X control and/or data message onthe corresponding subframe SF#N with a pre-defined or signaledprobability P (for example, the probability P may be configured orsignaled to be 1). Upon determination that the V2X transmission wirelessdevice actually performs V2X control and/or data message transmission onthe corresponding subframe SF#N, one of all the basic resource units inthe corresponding subframe SF#N may be randomly selected and the V2Xcontrol and/or data message transmission may be performed using thisselected resource unit. Additionally or alternatively, one of theresource units having a relatively small average detected/sensed energyvalue among all the basic resource units in the corresponding subframeSF#N may randomly selected and the V2X control and/or data messagetransmission may be performed using the selected one.

In another example, the transmission probability value P per a set ofbasic resource units may be configured or signaled for the wirelessdevice. Thus, the V2X transmission wireless device may be configured todetermine whether to perform the V2X control and/or data messagetransmission using each set of the basic resource units with anindependent probability P.

In one embodiment, transmission probability values may be configuredindependently, or partially or entirely differently between the sets ofbasic resource units.

Although the V2X control and/or data message transmission using aspecific set of basic resource units are probabilistically determined,the final/actual V2X transmission may only be achieved if thecorresponding specific set of basic resource units is determined to be aset of idle resource units.

In another example, when the [suggested method#2] described above isapplied, the transmission probability values per a set of idle resourceunits (or the transmission probability value per a set of basic resourceunits) may be configured or signaled partially or completely differentlyor independently between V2X messages/information/service types, and/orV2X signals/channels with different priorities.

The transmission probability value per a set of idle resource units (orthe transmission probability value per a set of basic resource units)may be configured or signaled to be relatively higher with respect toinformation on incident occurrence and/or event occurrence-basedinformation or V2X synchronization signal with relatively high prioritythan with respect to other information or other V2X signal/channel withlow priority.

[Suggested method#3] The V2X transmission wireless device may beconfigured to select a ‘backoff value’ (named as SEL_BACKVAL) within abackoff window size/range (which may be named “BACKOFF_SIZE” and may berepresented, for example, as [0, B−1]) as derived/updated usingpredefined rules or pre-signaled on a specific subframe SF#K. Then, theV2X transmission wireless device may be configured to change a level towhich the corresponding selected backoff value decreases based on thenumber of idle resource units in a subsequent subframe that includes ordoes not include the corresponding subframe SF#K.

For example, when the V2X transmission wireless device selects a backoffvalue (SEL_BACKVAL) of Q value (0≤Q≤B−1) on the SF#N−1 subframe, Q-2 maybe obtained in an SF#N subframe including two idle resource units.

In another example, if there is no idle resource unit in the specificsubframe, exceptionally, the wireless device may be configured to reducethe backoff value (SEL_BACKVAL) based on a pre-defined or pre-signaledvalue (e.g., 1).

In another example, even if there are multiple idle resource units in aspecific subframe, the wireless device may be configured to reduce thebackoff value (SEL_BACKVAL) according to a predefined or signaled value(e.g., 1), irrespective of the number of idle resource units.

In still another example, even if an idle resource unit exists in aspecific subframe, and when pre-defined or signaledinformation/channel/signal transmission cannot be performed (forexample, if a V2X control message transmission cannot be performed andonly a V2X data message transmission can be performed), the wirelessdevice may be configured not to decrease the backoff value(SEL_BACKVAL).

In another example, although the V2X transmission wireless device hasidle resource units in a specific subframe, backoff value (SEL_BACKVAL)reduction operation based on a number of idle resource units may beomitted in order to defer its V2X control and/or data messagetransmission.

When applying these rules, the V2X transmission wireless devicedeliberately assumes the number of idle resource units to be a value of‘0’ or removes determination based on the idle resource units in orderto defer its V2X control and/or data message transmission.

When the above [suggested method#3] is applied, in one example, if thereis no idle resource unit in the SF#N subframe with a value of ‘0’ or avalue of ‘negative integer’ of the backoff value (SEL_BACKVAL), the V2Xtransmission device may be configured as follows: the V2X control and/ordata message transmission may be performed on idle resource units in thenearest subframe immediately after the SF#N subframe. Additionally oralternatively, it may be desirable to omit the V2X control and/or datamessage transmission on the ‘SF#N’ subframe. Additionally oralternatively, a backoff value (SEL_BACKVAL) may be re-selected from thebackoff window size/range (BACKOFF_SIZE) of the SF#N subframe.Additionally or alternatively, one of the entire basic resource units ofthe ‘SF#N’ subframe may be randomly selected and then the V2X controland or data message transmission may be performed using the selectedunit. Additionally and alternatively, one of the overall basic resourceunits of the ‘SF#N’ subframe with a relatively small average detected orsensed energy value may be randomly selected, and the selected unit maybe used for the V2X control and/or data message transmission.

If the above [suggested method#3] is applied, in one example, when thereare ‘M’ idle resource units in the SF#N subframe whose backoff value(SEL_BACKVAL) has a value of ‘0’ or a value of ‘negative integer’, theV2X transmission device may be configured as follows: randomly selectingone of the ‘M’ idle resource units to perform V2X control and/or datamessage transmission, and/or randomly selecting one of the idle resourceunits having a relatively small average detected or sensed energy valueto perform the V2X control and/or data message transmission.

In another example, when the above [suggested method#3] is applied, theV2X transmission device may be configured to independently select thebackoff value *SEL_BACKVAL) for each basic resource unit set from thebackoff window size/range (BACKOFF_SIZE) in the specific subframe SF#K.

The V2X device may be configured to reduce the backoff value(SEL_BACKVAL) of the basic resource unit set only if the correspondingset of the basic resource units is determined to be a set of idleresource units.

In another example, the V2X device may be configured to change themaximum value of the backoff window size/range (BACKOFF_SIZE) from whichthe backoff value (SEL_BACKVAL) is selected in the specific subframeSF#K, based on the number of idle resource units in the correspondingsubframe SF#K.

For example, if there are 3 idle resource units in the SF#N subframe,the backoff window size/range (BACKOFF_SIZE) in the correspondingsubframe SF#K is [0, 3−1], the maximum value of the backoff windowsize/range (BACKOFF_SIZE) is ‘2=3−1’.

When the above [suggested method#3] is applied, in one example, thebackoff window size/range (BACKOFF_SIZE) or BACKOFF_SIZE maximumvalue/minimum value or SEL_BACKVAL reduction size may be partially orcompletely different or independently configured or signaled between theV2X message/information/service type and/or V2X signal/channel withdifferent priorities.

The backoff window size/range (BACKOFF_SIZE) maximum value may beconfigured or signaled to be relatively lower with respect toinformation on incident occurrence and/or event occurrence-basedinformation or V2X synchronization signal with relatively high prioritythan with respect to other information or other V2X signal/channel withlow priority. Alternatively, the backoff value reduction may beconfigured or signaled to be relatively larger with respect toinformation on incident occurrence and/or event occurrence-basedinformation or V2X synchronization signal with relatively high prioritythan with respect to other information or other V2X signal/channel withlow priority.

[Suggested method#4] When the [suggested method#3] described above isapplied, in one example, the backoff window size/range (BACKOFF_SIZE)‘[0, B−1]’ in the specific subframe SF#K may be changed/updated inaccordance with some or all of the flowing rules.

(Rule#4-1) In one example, if the V2X control and/or data messagetransmission is performed using idle resource unit(s) that are more orequal to the pre-defined or signaled threshold value (for example, ‘1’)in a pre-defined or signaled time interval/region, (in other words, ifthere are more idle resource units than the pre-defined or signaledthreshold value (for example, ‘1’) in a pre-defined or signaled timeinterval/region), the V2X device may be configured to reduce a maximumvalue of the backoff window size/range (BACKOFF_SIZE) in the ‘SF#K’subframe to a (B−1)/W (e.g., ‘W=2’) or to increase the maximum value ofthe backoff window size/range (BACKOFF_SIZE) in the ‘SF#K’ subframe to a(B−1)*R (e.g., ‘R=2’).

The corresponding time interval/region may be set to the intervalbetween SF#(K−T) and SF#(K−1) (for example, ‘T’ value is a positiveinteger equal to or greater than 1) or the interval between SF#(K−T1)and SF#(K−T2) (e.g., ‘T1’, ‘T2’ values may be configured as a positiveinteger greater than or equal to 1).

In one example, if the V2X control and/or data message transmission isperformed using idle resource unit(s) that are more or equal to thepre-defined or signaled threshold value (for example, ‘1’) in thepre-defined or signaled time interval/region, (in other words, if thereare more idle resource units than the pre-defined or signaled thresholdvalue (for example, ‘1’) in the pre-defined or signaled timeinterval/region), the V2X device may be configured to increase themaximum value of the backoff window size/range (BACKOFF_SIZE) in the‘SF#K’ subframe to a (B−1)*R (e.g., ‘R=2’) or reduce a maximum value ofthe backoff window size/range (BACKOFF_SIZE) in the ‘SF#K’ subframe to a(B−1)/W (e.g., ‘W=2’).

If the Rule#4-1 is applied, parameters (for example, ‘W’, ‘R’) used forchanging/updating the maximum value of the backoff window size/range(BACKOFF_SIZE) may be configured partially or totally differently orindependently between the V2X message/information/service type and/orV2X signal/channel with different priorities.

[Suggested method#5] When the [suggested method#3] described above isapplied, in one example, only the V2X transmission wireless devicesatisfying some or all of the following conditions may be configured toselect a backoff value from the backoff window size/range (BACKOFF_SIZE)([0, B−1]) as derived/updated using the predefined rule, or aspre-signaled in the specific subframe SF#K.

Condition#5-1: V2X transmission wireless device with backoff value of‘0’ or ‘negative integer’ value.

Condition#5-2: V2X transmission wireless device actually performing theV2X control and/or data message transmission before the ‘SF#K’ subframe;and/or V2X transmission wireless device that omits the V2X controland/or data message transmission before the subframe ‘SF#K’ according apredefined rule.

When some or all of the proposed schemes (for example, [suggestedmethod#1], [suggested method#2], [suggested method#3], [suggestedmethod#4], and [suggested method#5]) are applied, the V2X transmissionwireless device may be configured to perform the V2X control and/or datamessage transmission by performing the following procedure:

The PSCCH may be transmitted in one subframe or a plurality ofpre-defined or pre-signaled subframes. One PRB may be used in each slot.The set of PRB candidates which may be used for PSCCH transmission inthe first slot may be set to {PRB_(PSCCH, 0), PRB_(PSCCH, 1, . . .) ,PRB_(PSCCH, N−1)} which may be configured by an upper layer.

If the wireless device transmits the PSCCH using PRB_(PSCCH, X) in thefirst slot of the subframe, and the PSSCH (physical sidelink sharedchannel), which is a sidelink shared channel is to be transmitted by thewireless device on the subframe, the following condition should besatisfied.

0<PRB_(PSSCH, start)−PRB_(PSCCH, x)<A, or0<PRB_(PSCCH, x)−PRB_(PSSCH, end)<A.

In the above relationship, PRB_(PSSCH, start) denotes the smallest indexamong the indexes of PRBs used for PSSCH transmission, whilePRB_(PSSCH, end) indicate the largest index among the PRB indexes usedfor PSSCH transmission. “A” may be configured by the network or apredefined value.

The sidelink grant may include information indicating the SCI (sidelinkcontrol information) and the PSCCH transmission resource.

The wireless device with data to transmit may initiate a PSCCHtransmission procedure. The wireless device randomly selects a backoffvalue from interval [1, CWmax]. The wireless device determines the SCIinformation excluding the resource block assignment field and determinesthe L_(CRBs) value. In this connection, L_(CRBs) value may refer to thenumber of consecutive resource blocks allocated to the PSSCH (physicalsidelink shared channel).

Before starting the PSCCH transmission procedure, as long as all PRBs ofall subframes are included in the resource pool, the wireless deviceassumes that all PRBs of all subframes are available.

The wireless device monitors the PSCCH candidates on the subframe n-k.That is, by monitoring each PSCCH candidate on the subframe n-k, thewireless device may receive SCIs for other wireless devices.

The wireless device considers that the PRB used for transmission of thePSSCH scheduled via one of the SCIs for the other wireless devicesreceived on the subframe n-k is not-available.

If the subframe n is included in the PSCCH subframe pool indicating thecandidate subframes that may be used for transmission of the PSCCH, andthe PSCCH transmission using PRB_(PSCCH, x) in the first slot of thesubframe n does not use the unavailable PRB, that is, if PRB_(PSCCH, x)is an available PRB, the SCI transmission having the specific resourcebock assignment configuration based on the determined L_(CRBs) on thesubframe n does not use the unavailable PRB. When the subframe n isincluded in the PSSCH subframe pool, and the configuration of the PSSCHPRBs and the resource block assignment field satisfy the simultaneoustransmission conditions of the PSSCH and the PSCCH, the wireless deviceconsiders that the configuration of the side link grant and the resourceblock assignment including PRB_(PSCCH, x) for the PSCCH transmissionresource is feasible.

Otherwise, the wireless device assumes that the configuration of theside link grant and the resource block assignment includingPRB_(PSCCH, x) for the PSCCH transmission resource is either unfeasibleor feasible.

If there is at least one feasible side link grant, the wireless devicereduces the backoff value by one.

When the backoff value is zero, the wireless device may transmit thePSCCH according to the feasible sidelink grant on the subframe n. Ifthere is more than one feasible sidelink grant, then one of the aplurality of sidelink grants may be selected with an even probability.

Upon completion of the PSCCH transmission procedure, the wireless devicemay continue the PSSCH transmission procedure. After this, the proceduremoves to a next subframe.

FIG. 10 illustrates signaling between a first wireless device and a basestation in order to transmit a V2X message.

Referring to FIG. 10, the base station transmits a sidelinkconfiguration to the first wireless device and the second wirelessdevice at step S510.

The sidelink configuration may include information indicating thesubframes that the wireless device may use to transmit the PSCCH, i.e.,the PSCCH subframe pool. The PSCCH subframe pool information may beprovided in a bitmap form. Further, the sidelink configuration mayinclude information indicating the subframes that the wireless devicemay use to transmit the PSSCH, i.e., the PSSCH subframe pool. The PSSCHsubframe pool information may be provided in bitmap form. Further, thesidelink configuration may also include information indicating aresource block that may be used for PSCCH and/or PSSCH transmission. Allof information indicated by the PSCCH subframe pool, the PSSCH subframepool, or the PSCCH and/or PSSCH resource block pool may not necessarilybe included in the same sidelink configuration.

The first wireless device determines a subframe and a resource blockused to transmit the PSCCH and/or the PSSCH based on the sidelinkconfiguration at step S512. In this procedure, the first wireless devicemay use at least one of the above-mentioned suggested methods#1 to #5.In particular, when a plurality of idle resource units are given, atleast one of the above-mentioned suggested methods#1 to #5 may be usedto determine which idle resource unit is actually used.

The first wireless device transmits the PSCCH and/or the PSSCH to thesecond wireless device using the determined subframe and the resourceblock (S513). More specifically, the first wireless device may transmita PSCCH (e.g., which may be interpreted by the SCI) to the secondwireless device. After the PSCCH transmission, the first wireless devicemay transmit a PSSCH to the second device. Alternately, the first devicemay transmit the PSCCH and PSSCH to the second device on the samesubframe.

It is obvious that one example of the proposed scheme described abovemay be included as one of the implementation methods of the presentdisclosure and, therefore, may be considered as a kind of proposedschemes. Further, the proposed schemes described above may beimplemented independently, or may be implemented as a combination ofsome of the proposed schemes. In one example, the proposed scheme basedon the 3GPP LTE/LTE-A system has been described for convenience ofdescription in the present disclosure, but the range of the system towhich the proposed scheme is applied is different from the 3GPPLTE/LTE-A system. In one example, the proposed schemes according to thisdisclosure may be extended to D2D communication. D2D communication maymean that a wireless device and another wireless device communicateusing a direct wireless channel A wireless device may refer to a user'swireless device. A network device, such as a base station, may also beconsidered a wireless device if it transmits/receives signals accordingto a communication scheme between wireless devices.

FIG. 11 is a block diagram illustrating a wireless device in which anembodiment of the present disclosure is implemented.

Referring to FIG. 11, a wireless device 1100 includes a processor 1110,a memory 1120, and a radio frequency (RF) unit 1130. Processor 1110implements the above suggested functions, procedures and/or methods.

The RF unit 1130 is connected to the processor 1110 to transmit andreceive radio signals.

The processor may comprise an application-specific integrated circuit(ASIC), other chipset, logic circuitry and/or data processing device.The memory may include read-only memory (ROM), random access memory(RAM), flash memory, memory cards, storage media, and/or other storagedevices. The RF unit may include a baseband circuit for processing theradio signal. When the embodiment is implemented in software, theabove-described techniques may be implemented with modules (processes,functions, and so on) that perform the functions described above. Themodule may be stored in the memory and may be executed by the processor.The memory may be internal or external to the processor, and may becoupled to the processor by various well known means.

1. A method for performing a vehicle-to-everything, V2X (V2X) operationby a user equipment, UE, in a wireless communication system, the methodcomprising: monitoring a physical sidelink control channel, PSCCH, foran another UE on a first subframe; measuring a reference signal receivedpower, RSRP, on a physical sidelink shared channel, PSSCH, resourceregion scheduled by the PSCCH; and transmitting a V2X message for theanother UE on a second subframe using a resource that does not overlapwith a PSSCH resource, wherein the PSSCH resource is scheduled by thePSCCH and the RSRP measurement of the PSSCH resource is higher than athreshold.
 2. The method of claim 1, further comprising: receiving, froma network, information on a PSCCH subframe pool indicating subframeswhere the UE can transmit the PSCCH.
 3. The method of claim 2, whereinthe second subframe is included in the subframes indicated by theinformation on the PSCCH subframe pool.
 4. The method of claim 1,wherein monitoring a PSCCH for the another UE as moving a basic resourceunit composed of at least one subframe by one subframe.
 5. The method ofclaim 4, wherein the UE monitors an idle resource unit that does notoverlap with a resource scheduled by the PSCCH for the another UE. 6.The method of claim 5, wherein when a plurality of idle resource unitsare detected, the UE selects one idle resource unit among the pluralityof idle resource units and transmits a PSCCH.
 7. A user equipment, UE,for performing a vehicle-to-everything V2X (V2X) operation in a wirelesscommunication system, the UE comprising: a RF, radio frequency, unitconfigured to transmit and receive a RF signal; and a processoroperatively coupled to the RF unit, wherein the processor monitors aphysical sidelink control channel, PSCCH for an another UE on a firstsubframe, measure a reference signal received power, RSRP, on a physicalsidelink shared channel, PSSCH, resource region scheduled by the PSCCH,and transmits a V2X message for the another UE on a second subframeusing a resource that does not overlap with a PSSCH resource, whereinthe PSSCH resource is scheduled by the PSCCH and the RSRP measurement ofthe PSSCH resource is higher than a threshold.
 8. The UE of claim 7,wherein the UE receives, from a network, information on a PSCCH subframepool indicating subframes where the UE can transmit the PSCCH.
 9. The UEof claim 8, wherein the second subframe is included in the subframesindicated by the information on the PSCCH subframe pool.
 10. The UE ofclaim 7, wherein the UE monitors a PSCCH for the another UE as moving abasic resource unit composed of at least one subframe by one subframe.11. The UE of claim 10, wherein the UE monitors an idle resource unitthat does not overlap with a resource scheduled by the PSCCH for theanother UE.
 12. The UE of claim 11, wherein when a plurality of idleresource units are detected, the UE selects one idle resource unit amongthe plurality of idle resource units and transmits a PSCCH.